1. Technical Field
The present invention relates to optics, and more particularly relates to light beam transmission, especially laser beam transmission.
2. Background Art
Laser technology is steadily advancing and with each advance new problems are posed which demand still further advances. For example, a recent development in the field is the use of lasers in simulator model board type image generation systems.
Model board image generation systems have been employed for years in the simulator art. FIG. 1 shows the main elements of one such system for an aircraft simulator. A model board 10 comprising an extraordinarily detailed scale model of an extensive geographic area is mounted on one side, as shown. A gantry 12 is made to move back and forth on rails 14 while a frame 16 typically supports a camera which moves up and down and in and out on the gantry 12 thus providing the camera with full three-dimensional movement over the board 10. A small controllable mirror on the end of the camera provides attitudinal control over the camera viewing window.
More recently, and as shown in FIG. 1, a laser projector system has been developed to replace the camera. In this system a remote laser beam generator system 18 generates a beam 20 of "white" laser light made up of three or more monochromatic laser light components. This beam 20 is projected to a pair of mirrors 22, 24, which relay the beam 20 to a scanner mounted on the frame 16. The scanner scans the beam in the pattern of a TV raster onto the portion of the model board to be viewed, as depicted schematically by lines 26. A bank 28 of triads of photocells 30 having red, blue and green filters detect the light reflected off of the board 10 to thereby generate color video signals, all according to principles known in the art. The movement of the scanner about the board is controlled by a computer and associated drive circuitry, which might be located in cabinets 32, as shown, to coordinate the movement of the scanner with the computed movements of the aircraft being simulated. Video signals generated as described above are used in a video display system to provide the simulator operator with a realistic view as he would see from a real aircraft.
One major problem posed by the system just described is that of laser beam spatial stability. As the gantry 12 moves along the rails 14 and as the frame 16 moves on the gantry 12, vibrational motion is generated which is transmitted to the mirror 22, 24. The mirrors 22, 24, themselves warp with temperature change. Considering that a typical gantry must traverse across a lateral distance of some 60 feet, while the frame travels up and down through a range of some 24 feet, in and out excursion adding another 2 feet, even minor angular changes can cause serious lateral beam stability problems.
Accurate machining of gantry and frame moving parts and other refinements of the physical system can reduce these errors, but only to a point. Typical residual errors in a system such as described above are displacement errors of the order of one of five millimeters, and angular errors of the order of 0.05.degree.. While this may appear fantastically small compared to the gross traveling distances described above, it is unacceptable for TV stability and resolution demands for simulator applications. For example, desired displacement tolerances at the scanner input are of the order of a quarter of a millimeter or less.
The present invention solves this problem and provides a laser or other light beam transmission system for projecting a light beam across large distances while maintaining a high degree of beam spatial stability.